Ignition Timing Control

You can do both, as long as your willing to take the time to do the programing. Haltech has a few different options. For the easiest/best I would say just go with an AEM unit. I've been very happy with mine.

For just timing control look into the Apex'i ITC. It is a piggy back timing controller. The only one that I can think of actually.

the perfect power SMT-7 can also control timing. it also has an option to get rid of the MAS altogether and run the system as speed density. not sure if it can handle karmann meters though- it might be voltage only.

i've been toying with a few circuits that can modify output pulse width.. this would allow a tuner to change the output side of the ECU to compensate for larger injectors instead of screwing with the load signal, so you can modify fuel as much as you want and leave the timing maps intact.